Dave, I think Terry got the best study case: (1) field failure (2) assembly failure and (3) HALT failure. If the induced HALT failure got different failure mode, I guess he better forget the HALT. (I mean not define the functional failure mode, but physical failure mode. such as via saperation, etc.etc.). jk >-----Original Message----- >From: TechNet [mailto:[log in to unmask]]On Behalf Of Dave Hillman >Sent: Tuesday, July 16, 2002 5:53 PM >To: [log in to unmask] >Subject: Re: [TN] Stress screening of multi layer production boards for >optimum reliability > > >Hi Werner! Terry is describing a HASS (highly accelerated stress screen) or >a HALT (highly accelerated life test) type of chamber. We have six of the >HASS chambers which are used to improve printed wiring assembly design >robustness (we track what fails, determine if that failure mode/mechanism >is valid for the use environment and make any appropriate design >improvements). These chambers can indeed provide temperature ramp rates of >5-50C per minute (they use LN2 boost) - the ultimate in thermal shock >recipes. I think you raised the most important questions - what is the >relationship of the failure modes/mechanisms induced by the HALT chamber >and the failure mechanisms the printed wiring assembly undergoes in its use >environment? Pretty tough question. > >Dave Hillman >Rockwell Collins >[log in to unmask] > > > > >Werner Engelmaier <[log in to unmask]>@ipc.org> on 07/16/2002 07:25:49 AM > >Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond > to [log in to unmask] > >Sent by: TechNet <[log in to unmask]> > > >To: [log in to unmask] >cc: > >Subject: Re: [TN] Stress screening of multi layer production boards for > optimum reliability > > >Hi Terry, >>My thermal stressing uses the following parameters: >>10 cycles of hot / cold exposure in a HALT chamber, >>-60 deg C to +120 deg C temperature excursions, >>40 deg C per minute temperature ramp rate. >>The boards are electrically tested after thermal stressing. >A: The ramp rate surely is not correct. What exactly is a "HALT" chamber? >Depending on the nature of the failures you experience, your testing is not >much of an ESS, and electrically testing after, not during, thermal >stressing >will show little even if latent defects are precipitated to failure. >>I calculate the screening is using approximately 20% of the expected life >of >the >>assembled boards, so I am reluctant to increase the stress levels. >A: On the basis of what model do you make this calculation? You do nopt >even >have a failure mode, let alone a root-cause failure mechanis. >>My board manufacturer has made several process improvements over the last >year but >>I have not seen a significant improvement in my assembly yield. >A: Again. without knowing what is really happening, what the design details >are, and how these PCBs are used, it is impossible to make concrete >recommendations. > >Werner Engelmaier >Engelmaier Associates, L.C. >Electronic Packaging, Interconnection and Reliability Consulting >7 Jasmine Run >Ormond Beach, FL 32174 USA >Phone: 386-437-8747, Fax: 386-437-8737 >E-mail: [log in to unmask], Website: www.engelmaier.com > >------------------------------------------------------------------- >-------------- > >Technet Mail List provided as a free service by IPC using LISTSERV 1.8e >To unsubscribe, send a message to [log in to unmask] with following text in >the BODY (NOT the subject field): SIGNOFF Technet >To temporarily halt or (re-start) delivery of Technet send e-mail to >[log in to unmask]: SET Technet NOMAIL or (MAIL) >To receive ONE mailing per day of all the posts: send e-mail to >[log in to unmask]: SET Technet Digest >Search the archives of previous posts at: http://listserv.ipc.org/archives >Please visit IPC web site http://www.ipc.org/html/forum.htm for additional >information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 >ext.5315 >------------------------------------------------------------------- >-------------- > >------------------------------------------------------------------- >-------------- >Technet Mail List provided as a free service by IPC using LISTSERV 1.8e >To unsubscribe, send a message to [log in to unmask] with following text in >the BODY (NOT the subject field): SIGNOFF Technet >To temporarily halt or (re-start) delivery of Technet send e-mail >to [log in to unmask]: SET Technet NOMAIL or (MAIL) >To receive ONE mailing per day of all the posts: send e-mail to >[log in to unmask]: SET Technet Digest >Search the archives of previous posts at: http://listserv.ipc.org/archives >Please visit IPC web site http://www.ipc.org/html/forum.htm for additional >information, or contact Keach Sasamori at [log in to unmask] or >847-509-9700 ext.5315 >------------------------------------------------------------------- >-------------- > --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------